Chapter 16 Thermal Energy and Heat

16.1 Thermal Energy and Matter

KEY CONCEPTS In what direction does heat flow spontaneously? What is the temperature of an object related to? What two variables is thermal energy related to? How is a change in temperature related to specific heat? On what principle does a calorimeter operate?

When drilling out brass cannons, Count Rumford concluded that heat is not matter, and that it is related to work. Where did the heat come from when the Count allowed the turnings from drilling fall into the water?

Recall that THERMAL ENERGY is the sum of the kinetic and potential energy of the particles in an object HEAT is the transfer of thermal energy because of a temperature difference; heat spontaneously flows from HOT TO COLD

TEMPERATURE is a measure of how hot or cold something is compared to a reference point Ex. Celsius scale is based on m.p. and b.p of water; Kelvin scale is based on ABSOLUTE ZERO-temp. at which all particle motion stops Temperature is related to the average kinetic energy of the particles in an object; the higher the temperature, the greater the kinetic energy of the particles

Thermal energy depends on 1. MASS-greater mass means more particles to have PE and KE 2. TEMPERATURE-higher temperatures means greater average KE of particles 3. PHASE-PE of particles in gaseous state is greater than in liquid state, which is greater than in solid state

Which has more thermal energy: a. a cup of water at 20 o C or a bathtub of water at 20 o C? b. ten grams of liquid water at 20 o C or 10 g of water vapor at 20 o C? c. ten grams of water at 20 o C or 10 g of water at 40 o C? If a car sits in the sun for 4 hours, which will be at a higher temperature-a metal part or a plastic part that received the same amount of sunlight?

SPECIFIC HEAT is the amount of heat needed to raise the temperature of one gram of a material by 1 o C Which has the lower specific heat in the previous example-the metal or the plastic? Note that the lower the specific heat of a material, the greater the temperature change when a given amount of energy is absorbed by a given mass

Specific heat (c) is usually measured in J/g.o C SEE FIG. 3, P. 476 Specific heat is related to the temperature change, heat gained or lost, and mass of the material by Q = mc∆T where Q is heat gained/lost (in J), m is mass (in g), c is specific heat (in J/g o C), and ∆T is change in temperature (∆T = T f – T i ) SEE “MATH PRACTICE” P. 477

A CALORIMETER is an instrument used to measure changes in thermal energy SEE FIG. 4, P. 478 A calorimeter uses the principle that heat will flow from a warmer to colder object until they reach the same temperature-THERMAL EQUILIBRIUM Worksheet problems SEE SECTION 16.1 ASSESSMENT, P. 478

16.2-Heat and Thermodynamics

KEY CONCEPTS Why is conduction slower in gases than in liquids or solids? In what natural cycles do convection currents occur? How does an object’s temperature affect radiation?

CONDUCTION is the transfer of energy through matter by direct contact of particles; occurs within materials or between materials that are touching Ex. Newton’s cradle; SEE FIG. 5, P. 479 Note that conduction in gases is slower than in liquids or solids-WHY?

A THERMAL CONDUCTOR is a material that conducts thermal energy well Ex. metal A THERMAL INSULATOR is a material that conducts thermal energy poorly Ex. glass, air

CONVECTION is the transfer of thermal energy by the movement of particles of a fluid from one place to another Ex. convection demo; SEE FIG. 7, P. 480 Examples of transfer of thermal energy by convection currents include 1. Ocean currents 2. Weather systems 3. Magma in Earth’s interior

RADIATION is transfer of thermal energy by electromagnetic waves; does NOT require matter to be present Ex. radiation from the sun; SEE FIG. 8, P. 481 Note that all objects radiate energy; the higher the temperature, the greater the rate at which energy is radiated SEE SECTION 16.2 ASSESSMENT, P. 483